The present invention relates to a drill chuck. More particularly this invention concerns such a chuck which can be used with both smooth- and hex-shank bits.
A basic drill chuck has a chuck body centered on and rotatable about an axis and formed with an axially centered and axially forwardly open tool-receiving recess. A plurality of jaws angularly spaced about the recess can be moved axially forward and radially inward to grip a smooth-shank tool bit engaged in the recess. Normally a ring on sleeve on the chuck body is rotated to effect this jaw movement. The jaws are either carried in angled guide passages formed in the chuck body and have toothed outer edges meshing with a screwthread of the tightening ring, or are carried in angled guide passages formed in the ring and have toothed inner edges meshing with a screwthread of the chuck body.
It is also known to provide structure at the rear end of the tool recess that forms a standardized hexagonal seat that is open axially forward and that is rotationally coupled to, if not actually formed by, the chuck body. This seat has a diagonal measurement of 6.35 mm and is intended to received the similarly dimensioned hex shanks of various tools, in particular screw bits. Thus although it is possible to solidly grip a hex-shank bit in the standard three-jaw chuck, the supplemental hex seat makes it possible to more quickly mount and accurately hold a hex-shank bit. A spring-loaded retainer is provided to hold such hex-shank bits, so that they can be easily snapped into and out of the chuck.
The hex seat at the rear end of the tool recess is not a problem when the chuck is used with relatively large-diameter smooth-shank bits. The shanks of such bits cannot fit into the hex seat so the rear end of the tool sits atop this seat.
When, however, a smaller-diameter bit is being chucked, for instance one having a smooth shank smaller than 6 mm in diameter, it is possible for it to extend back into the hex seat. This is disadvantageous in that it allows the bit to fit too deeply into the chuck so that the jaws, for instance, will come into engagement with the actual cutting flute of the tool and possible damage it. Furthermore when tools of about 6 mm in diameter are being chucked, they can jam in and actually damage the hex seat.
It is therefore an object of the present invention to provide an improved chuck for hex- and smooth-shank bits.
Another object is the provision of such an improved chuck for hex- and smooth-shank bits which overcomes the above-given disadvantages, that is which protects the hex seat.
A drill chuck has according to the invention a chuck body centered on an axis and forming an axially forwardly open bit-receiving recess, an axially forwardly open polygonal-section seat at a base of the recess, and a plurality of jaws spaced angularly around the recess forward of the seat. The jaws can be displaced radially inward and outward to grip a bit in the recess. An element can move in the base of the recess between a blocking position in front of the polygonal-section seat and preventing entry of a bit thereinto and a freeing position clear of the seat and permitting entry of a bit thereinto. This element can be actuated for movement between the blocking and freeing positions either manually or automatically.
Thus with this arrangement the hex seat can be blocked to prevent a smooth-shank bit from fitting into it. This preserves the seat and the smooth-shank bits, and can even prevent large particles from lodging in the seat.
According to the invention the element is actuated by a ring rotatable about the axis on the chuck body. The element is a pin braced against the ring and generally radially displaceable in the chuck body. The ring has a cam surface against which the pin is braced and the cam surface can have one end forming a seat in which the pin is engageable in the blocking position. A spring urges the element against the surface and into the freeing position although it is possible for the pin to have a formation positively coupling it to the jaw for synchronous movement without the spring. For most efficient blocking of the seat there are a plurality of the pins angularly equispaced around the axis.
Alternately in accordance with the invention the element includes a lever pivoted about a lever axis on the chuck body. This lever can be coupled to a pin itself movable in front of the seat in the blocking position. It is also possible for the lever itself to have an end movable in front of the seat in the blocking position.
The chuck body according to the invention is formed with angled guides holding the jaws and a ring rotatable about the axis on the body has a screwthread meshing with the jaws so that rotation of the ring displaces the jaws axially and radially. One of the jaws can be formed with a cam face engageable with the lever for displacing the lever end into the blocking position on axial advance of the one jaw past a predetermined position. In another arrangement the element is a plate slidable in the chuck body transverse to the axis and formed with an aperture aligned with the seat in the freeing position. One of the jaws is formed with a cam face engageable with the plate for displacing the aperture out of alignment with the seat on axial advance of the one jaw past a predetermined position. A spring urges the plate against the face of the one jaw. The element can also be a leaf spring bearing elastically against one of the jaws and having an end displaceable in front of the seat on axial forward advance of the one jaw past a predetermined position.
One of the jaws according to the invention can have a notch in which is engageable a spring-biased element when the jaw is in a predetermined position. When this or another one of the jaws is formed with a cam surface engageable with the element to displace it between the blocking and freeing positions, this predetermined position corresponds the blocking position of the element. This gives the user the ability, when closing the chuck to feel when the blocking position is set and can serve to hold the chuck in the seat-blocked position.
The polygonal seat, which normally is hexagonal and corresponds to the standard screw bit can be formed in the chuck body or can be formed in the spindle or, more likely, in an element carried on the spindle so that hex-shank tools are actually virtually directly coupled to the power-unit spindle. The element on the spindle forming the hex shank is typically a small socket that can move axially limitedly relative to the spindle and that is biased axially forward to push the bit out.